1. Field of the Invention
The present invention relates to a tire condition detecting device, a tire condition monitoring system, and a method of attaching a tire condition detecting device to a tire wheel.
2. Description of the Related Art
FIG. 8 shows an example of a tire condition monitoring system. Conventionally, there is a tire condition monitoring system comprising a tire condition detecting device 1 provided on each tire wheel 10 and having a sensor and transmission section 2, a receiving antenna and a receiver 21 provided on a vehicle, and a meter 22 provided in a vehicle compartment.
In such a tire condition monitoring system, the condition of each tire, such as air pressure and temperature within a tire is transmitted by radio waves from the sensor and transmission section 2, the radio waves are received by the receiver 21 through the receiving antenna and, after data processing is carried out in a control circuit of the receiver 21, the condition of each tire is displayed in the meter 22. (For example, refer to Patent document 1).
Various types of tire condition detecting device 1 are available in the market, such as a valve-integrated type or a type in which the tire condition detecting device 1 is fixed on a wheel with a metal belt. FIGS. 9A, 9B, and 10 each show the tire condition detecting device 1.
In the case of the tire condition detecting device 1 of a valve-integrated type, the sensor and transmission section 2, and a battery 25 are contained in a case 24 provided to a valve 23 as shown in FIG. 9A. Then, as shown in FIG. 9B, the case 24, in which the sensor and transmission section 2 is contained, is attached to a valve hole of a rim 12 in a state in which the case 24 is arranged in an area, in which air is present, between the rim 12 of the wheel 10 and a tire 14, that is, in an air chamber 15.
In the case of the tire condition detecting device 1 that is fixed on a wheel with a metal belt, the sensor and transmission section 2 is contained in a case 32 fixed on a metal belt 31, as shown in FIG. 10. Then, the case 32 in which the sensor and transmission section is contained is fixed on the outer surface of the rim 12, that is, a surface 12b of the rim 12 on the side of the air chamber 15 with a metal belt 31.
[Patent document 1]
Japanese Unexamined Patent Publication (Kokai) No. 2002-257661
In the two tire condition detecting devices 1 with the structures described above, each of the transmission sections 2 is arranged in the air chamber 15. Because of this, the two tire condition detecting devices 1 having these two type structures cause a problem in that the radio waves transmitted from the transmission section 2 are attenuated while passing through tires or wheels.
Generally, the wheel 10 is made of metal such as aluminum or steel. A radial tire has, in general, a body ply made of polyester or the like for supporting the entire structure and a steel ply arranged on a tread surface. However, in the case of some types of a tire, in addition to the tread surface, the side surfaces are configured of steel plies.
When the entire structure of the tire 14 is configured by metal such as in the case where not only the tread surface but also the side surface is configured of a steel ply, radio waves are unlikely to pass through the metal and the above-mentioned problem becomes more serious. Moreover, the amount of metal contained in the tire 14, etc. differs from type to type. Because of this, depending on the types of the tire 14, there is produced a variation in the degree of attenuation of the radio waves transmitted from the transmission section, leading to a variation in the level of the radio waves received by the receiver.